enemy, may, through the shelter which, in case of necessity, the walls of a fortress afford them, be able to maintain themselves in the country, and to a certain extent to command it.
The enterprises which the garrison of a fortress can venture to undertake are always somewhat restricted. Even in the case of large places and strong garrisons, the bodies of troops which can be employed on such operations are mostly inconsiderable as compared with the forces in the field, and their average sphere of action seldom exceeds a couple of days’ marches. If the fortress is small, the detachments it can send out are quite insignificant and the range of their activity will generally be confined to the nearest villages. But corps which do not belong to the garrison, and therefore are not under the necessity of returning to the place, are thereby much more at liberty in their movements, and by their means, if other circumstances are favourable, the external zone of action of a fortress may be immensely extended. Therefore if we speak of the active influence of fortresses in general terms, we must always keep this feature of the same principally in view.